We showed recently that the soil yeast Trichosporon cutaneum grows well at the expense of a wide range of aromatic acids biochemically related to phenylalanine and tyrosine (Anderson and Dagley. 1980. J. Bact. 141:534-543). Enzymes for catabolizing L-tryptophan were also derepressed by some of these compounds. The pathway used by this organism for L-tryptophan as major carbon source will be elucidated and some of the enzymes will be purified and characterized. The enzyme L-threo-beta-phenylserine dehydratase (deaminating) has been purified from a coryneform soil organism; its mechanism of action will be investigated. Tyrosine-related biochemicals support the growth of certain strains of Escherichia coli; pathways will be delineated and enzymes purified for comparison with those used by pseudomonads.